JP3272230B2 - Blue light emitting polymer and method of manufacturing blue light emitting diode using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blue light emitting polymer and a light emitting diode using the same, and more particularly, to a blue light emitting polymer capable of emitting blue light for a long time and having excellent light emission efficiency. And a light emitting diode employing the same.

[0002]

2. Description of the Related Art Conjugated polymers
Has electrical, non-linear optical and luminescent properties. Further, polymers are excellent in workability and low in cost as compared with metals and semiconductors. Therefore, research on application of conjugated polymers is being actively conducted in the electric / electronic industry.

However, most of the conjugated polymers currently developed have poor solubility, and if the length of the spacer group consisting of the alkyl group in the main chain is increased in order to increase the solubility, the mechanical properties will increase. There is a problem that the characteristic is impaired and the application is limited. Therefore, electrical conductivity,
Researches on conductive polymers having not only nonlinear optical response characteristics and emission characteristics but also excellent workability are being actively conducted.

On the other hand, current liquid crystal display devices (LCDs)
Although it is widely used because of its advantage of low power consumption and light weight, it is difficult to increase the size and color. Due to the limitations of such a liquid crystal display device, a light-emitting diode (hereinafter, referred to as an LED) is used.
There has been increasing interest in display devices that employ.

A display device employing a light-emitting diode has much better responsiveness and contrast than a light-receiving type liquid crystal display device, and therefore can replace a cathode ray tube and a liquid crystal display device which is a flat panel type display device. It is expected.

[0006] Most of the light emitting diodes currently used are made of inorganic crystals, but it is difficult to reduce the power, color and size of the light emitting diodes made of such inorganic materials, and the driving voltage is high. And it is difficult to obtain light in the green and blue regions.

Therefore, in order to overcome the limitations of inorganic crystals, research on organic polymer materials as materials for light emitting diodes has been concentrated. Research on polymer-based light-emitting diodes was first published by the Cambridge group in the UK in 1990 (US Pat. No. 5,247,190). The polymer substance used as the light-emitting layer is poly (1,4-phenylenevinylene) having a conjugated double bond, and is represented by the following formula (I).

[0008]

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The poly (1,4-phenylene vinylene)
Is a conjugated polymer in which a phenyl group and a double bond are alternately linked, emits green light at a wavelength of 540 nm, and is 0.01% when aluminum and ITO (Indium Tin Oxide) are used for a cathode and an anode, respectively. % Luminous efficiency.

[0010] Subsequently, a study on poly (1,4-phenylenevinylene) (PPV) and its derivatives was conducted by the Cambridge Group and the Heeger Group (US Santa Barbara) (WO 9216023).
It was reported that the luminous efficiency was improved to about 4% through the development of various electrodes and a new light emitting layer (Nature 1993, 365,
628). However, since PPV and its derivatives have a complete conjugated double bond, there is a disadvantage that light having a wavelength region below green cannot be obtained.

As a result, research on the development of blue light-emitting polymers has been concentrated, and it has been announced that polyparaphenylene (PPP) emits blue light at 459 nm or less (Synth. Met. 1992, 51 383), and that It was announced that Floren exhibits a blue color at 470 nm (Jpn.
J. Appl. Phys. 1991, 30 , L1941). However,
The synthesis of PPP and alkyl fluorene is difficult, and the quality and processability of the film are deteriorated, so that the lifetime of light emission is very short.

On the other hand, a blue light emitting polymer (II) having a constant conjugated double bond unit made of phenylene vinylene has been developed by Karasz group of Massachusetts Institute of Technology (MIT) in the United States and the like.

[0013]

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It has been reported that the polymer represented by the above formula (II) is dissolved in an organic solvent and has excellent processability and film quality (Macromolecules 1993).
, 26 , 1188). However, when such a polymer is used as a luminescent material, there is a problem that the length of a spacer group added to increase the solubility is large and excellent mechanical properties of PPV are impaired.

JP-A-5-320635 discloses the synthesis of a blue-green and blue-emitting polymer represented by the following formula (III).

[0016]

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The most main part of the polymer represented by the formula (III) is an Ar ₂ unit, and the Ar ₂ unit has a form in which phenylene is symmetrically substituted with an alkoxy group. However, the alkoxy group is a strong electron donating group.
g group), it acts to shift the wavelength of the emitted light to the longer wavelength side by shifting the polymer absorption wavelength to the longer wavelength side. Therefore, the emission wavelength of the substituted polymer of the alkoxy group is 520 to 530 nm,
It will be located in the blue-green region where green color is darkened.

On the other hand, when the Ar ₂ unit is phenyl, naphthalene, biphenyl or the like having no substituent, the emission wavelength shifts to the shorter wavelength side, but the solubility of the polymer is not good.

On the other hand, if the number of spacer groups is increased in order to increase the solubility, the thermal stability of the film is poor and the life is shortened, so that there is a problem that its application is difficult. Therefore, there is an increasing need for a blue light emitting polymer substance having high solubility in organic solvents.

On the other hand, FIG. 1 schematically shows a general light emitting diode. Generally, a positive electrode 2 is formed on a substrate 1 by a method such as thermal evaporation, and a thin film type polymer is formed thereon. After the film 3 is formed, the negative electrode 4 is formed. In this case, in forming a polymer film, it is common to dissolve a polymer substance or a polymer precursor in a solvent and then perform spin coating. However, if the solubility of the polymer or the polymer precursor is not good, there is a problem that not only the formation of the polymer film is not easy but also the luminous efficiency of the formed polymer is not good.

FIG. 2 schematically shows a process of performing electroluminescence when an electric field is applied to the light emitting diode as shown in FIG. As can be seen from FIG. 2, when an electric field is applied through each electrode of FIG. 1, negative and positively charged polarons (polaron, p ⁻ , p ⁺ ) are generated due to the structural relaxation action of the polymer chain. Immediately after forming polaron-excitons, light is emitted while recombining a single polaron-exciton in a very short time.

However, if there is a flaw in the polymer, the flaw is the center of recombination that does not emit light. Such scratches are generated in the process of using a polymer having poor solubility, and there is a problem that a light emitting diode manufactured using a polymer having poor solubility has poor luminous efficiency.

[0023]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a blue light-emitting polymer which can solve the above-mentioned problems and can emit light in a blue region for a long time and has excellent workability. It is in.

It is another object of the present invention to provide a blue light emitting diode which can emit light in a blue region for a long time and has excellent thermal stability.

In order to achieve the above object, the present invention provides:
It is represented by the following general formula (IV) and has a weight average molecular weight of 58
The present invention provides a blue light-emitting polymer having a molecular weight of from 00 to 13000 .

[0026]

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In the general formula (IV), X is the following formula (V) or (VI) , and X is the following:
In the case of the formula (V), Y is the following general formula (VII) or
Is (VIII) ; Z is the following formula (V ): n
Is 3, m is 5-100 der Ri; is X, the following formula
In the case of (VI), Y is represented by the following general formula (VII) or
Is (VIII), Z is the following formula (IX),
n is 5 and m is 5-100.

[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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However, the general formulas (VII) and (VII)
In I), R ₁ , R ₂ and R ₃ are each a methyl group .

In particular, X in the general formula (IV) is
In the case of the formula (V), n is 3, and X is
In the case of (VI), n is 5 , and the general formula (VI
R ₁ , R ₂ and R _{3 in} I) and (VIII) are respectively
Those which are methyl groups are desirable.

According to another aspect of the present invention, there is provided a light emitting diode including a positive electrode layer, a negative electrode layer, and a polymer layer formed between the two electrode layers. According to another aspect of the present invention, there is provided a blue light emitting diode comprising a conjugated polymer represented by the general formula (IV) and having a weight average molecular weight of 5800 to 13000 as a layer.

According to another aspect of the present invention, there is provided a blue light emitting diode, wherein the positive electrode is one selected from the group consisting of gold, platinum and ITO. Is what you do.

According to another aspect of the present invention, there is provided a blue light emitting diode, wherein the negative electrode is one selected from the group consisting of aluminum, magnesium and calcium. Is what you do. According to another embodiment of the present invention, there is provided a blue light emitting diode, wherein at least one of the positive electrode layer and the negative electrode layer is transparent. Things.

In the present invention, a blue light-emitting polymer represented by the aforementioned general formula (IV) and having a weight average molecular weight of 5800 to 13000 (or a conjugated polymer used for a polymer layer of a blue light-emitting diode) is used. Phenylene replaced by a silicon-containing group is contained in the main chain. In other words, silicon can emit blue light at a wavelength much shorter than that of a conventional alkoxy-substituted polymer, because silicon has similar electrical properties to donate or pull electrons to hydrogen atoms. In addition, unlike a polymer having no substituent, it has excellent solubility in organic solvents such as chloroform, dichloromethane, tetrahydrofuran, and cyclohexanone, and therefore, it is easy to form a uniform and less scratched polymer thin film. In addition, since the solubility is good even if the spacer group is short, mechanical strength and thermal stability similar to PPV can be maintained.

[0039]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to a blue light emitting polymer and a method of manufacturing a light emitting diode using the same.

Synthesis of Monomer (1) 2,5-bis (trialkylsilyl) -1,4
Synthesis of -xylenebis (triphenylphosphonium bromide) (X) As shown in the following formula, 2,5-bis (trialkylsilyl) -1,4-bis (bromomethyl) benzene and triphenylphosphine are reacted with DMF. After which it is precipitated with diethyl ether. Subsequently, the precipitate is filtered and dried under vacuum to obtain white 2,5-bis (trialkylsilyl) -1,4-xylenebis (triphenylphosphonium bromide) (X).

[0041]

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(2) 2-trialkylsilyl-1,4
Synthesis of -Xylenebis (triphenylphosphonium bromide) (XI) 2-trialkylsilyl-1,4-
Bis (bromomethyl) benzene and triphenylphosphine are reacted with DMF, and then precipitated with diethyl ether. Then, the precipitate is filtered and dried under vacuum to obtain a white product represented by the following formula (XI).

[0043]

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[0044] (3) bi scan (4-formyl - phenoxy) as in Equation following synthetic alkanes, 4-hydroxybenzaldehyde (hydroxybenzaldehyde) and both ends alkanes replaced with a bromine respectively (dibromo alkane) carbonate After reacting with a DMF solution in which potassium is dissolved, the mixture is cooled and precipitated. Next, the precipitate is filtered and dried in vacuo, and the precipitate is recrystallized in ethanol to obtain a white product represented by the following formula (XII).

[0045]

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[0046] (4) bi scan (4-formyl-2,6-dimethoxy-phenoxy) as in Equation following synthetic alkanes, 4-hydroxy-3,5-dimethoxy
The reaction of cybenzaldehyde and an alkane (dibromoalkane), each of which is replaced by one bromide, with a solution of potassium carbonate in DMF is allowed to cool and precipitate. Then, the precipitate was filtered and dried under vacuum,
The precipitate was recrystallized in ethanol to obtain the following formula (XII)
The white product shown in I) is obtained.

[0047]

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Synthesis of Polymeric Substance (1) Synthesis of P-1 As shown in the following formula, the same equivalents of (X) and (XII) monomers were completely dissolved in ethanol and chloroform solvents, and then a slight excess was obtained. Add sodium ethoxylate and react at room temperature. Next, the reaction product is extracted with chloroform and then precipitated in methanol to obtain a final polymer represented by P-1.

[0049]

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(2) Synthesis of P-2 When the same equivalents of the monomers (XI) and (XII) are used and the process (1) is performed, the final polymer represented by P-2 is obtained. can get.

[0051]

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(3) Synthesis of P-3 When the same equivalents of the monomers (X) and (XIII) are used and the above step (1) is performed, the final polymer represented by P-3 is obtained. can get.

[0053]

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(4) Synthesis of P-4 When the same equivalents of the monomers (XI) and (XIII) are used and the process (1) is carried out, the final polymer represented by P-4 is obtained. can get.

[0055]

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Manufacturing of Light Emitting Diode Using the polymer manufactured according to the present invention, a light emitting diode having a MIS (metal-semiconductor-metal) structure as shown in FIG. 1 is manufactured. In this case, the positive electrode of the light emitting diode is gold, platinum, I
The negative electrode is preferably made of aluminum, magnesium, calcium or the like having a relatively low work function.

In this case, at least one of the positive electrode and the negative electrode should be transparent in order to easily transmit emitted light.

[0058]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not necessarily limited to these examples.

Synthesis of Monomer 1) Synthesis of 2,5-bis (trimethylsilyl) -1,4-xylenebis (triphenylphosphonium bromide) 7.4 g of 2,5-bis (trimethylsilyl) -1,4
-Bis (bromomethyl) benzene was reacted with 4.3 g of triphenylphosphine in 30 ml of DMF for 24 hours. The reacted solution was precipitated with diethyl ether to obtain a white precipitate. The precipitate was filtered and dried under vacuum to obtain a final product represented by the following formula (X-1) (89% yield).

Melting point: 299-300 ° C. ¹ H-NMR (DMSO-d ₆ ): δ 7.94-7.
55 (m, 30H), 7.05 (s, 2H), 5.01
(D, 4H), -0.31 (s, 18H) Elemental analysis: Calculated (C 64.35%, H 5.79).
%), Measured values (C 63.01%, H 6.04%)

[0061]

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2) Synthesis of 2-trimethylsilyl-1,4-xylenebis (triphenylphosphonium bromide) 30 ml of 3.0 g of 2-trimethylsilyl-1,4-bis (bromomethyl) benzene and 5.2 g of triphenylphosphine Of DMF for 24 hours. The reacted solution was precipitated with diethyl ether to obtain a white precipitate. The precipitate is filtered and dried under vacuum to give the following formula (XI)
-1) was obtained (yield: 80).
%).

Melting point: 233-235 ° C. ¹ H-NMR (DMSO-d ₆ ): δ 7.91-7.
49 (m, 30H), 7.25 (s, 1H), 6.78
(D, 1H), 6.65 (d, 1H), 5.80 (d, 1H)
2H), 5.01 (d, 2H), -0.15 (s, 9
H) Elemental analysis: Calculated value (C 65.56%, H 5.36)
%), Measured values (C 61.85%, H 5.33%)

[0064]

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3) Synthesis of 1,3-bis (4-formyl-phenoxy) propane 10.0 g of 1,3-dibromopropane and 4 -hydroxy
Sibenzaldehyde was reacted with 100 ml of DMF in 6.2 g of potassium carbonate solution while refluxing for 24 hours.
The reaction mixture was precipitated in cold distilled water, then filtered and dried in vacuo. The obtained compound was recrystallized in ethanol to obtain a white product represented by the following formula (XII-1) (yield: 76%).

Melting point: 129 to 130 ° C. ¹ H-NMR (200 MHz, CDCl ₃ ) δ 9.
80 (s, 2H), 7.91 (s, 2H), 7.79
(D, 4H), 6.83 (d, 4H), 4.22 (t,
4H), 2.30 (q, 2H) ¹³ C-NMR (CDCl ₃ ) δ 190.7, 16
3.7, 131.9, 130.0, 114.6, 64.
4, 28.8 Elemental analysis: Calculated value (C 71.82%, H 5.67)
%), Measured values (C 70.43%, H 5.60%)

[0067]

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4) Synthesis of 1,5-bis (4-formyl-2,6-dimethoxyphenoxy) pentane 10.0 g of 4-hydroxy -3,5-dimethoxybenzaldehyde and 6.3 g of 1,5-Dibromopentane was added to 100 ml of DMF and 6.2 g of potassium carbonate solution.
The reaction was carried out while refluxing for 4 hours. The reaction was precipitated in cold distilled water, then filtered and dried under vacuum. The obtained compound was recrystallized from ethanol to obtain the following formula (XIII)
A white product represented by -1) was obtained (yield: 60%).

¹ H-NMR (200 MHz, CDC
l ₃ ) δ 9.82 (s, 2H), 7.08 (s, 2
H), 4.05 (t, 4H), 3.86 (s, 12
H) 1.93-1.71 (m, 4H), 1.61
(M, 2H) Elemental analysis: Calculated value (C 71.82%, H 5.67)
%), Measured values (C 70.43%, H 5.60%)

[0070]

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Example 1 Polymer Synthesis 3.28 g of 2,5-bis (trimethylsilyl) -1,
4-Xylenebis (triphenylphosphonium bromide) (X-1) and 1.00 g of 1,3-bis (4-formyl-phenoxy) propane (XII-1) (identical equivalent) were added to ethanol and 20 ml of chloroform solvent. After the mixture was completely dissolved, 0.6 g of sodium ethoxylate was added thereto and reacted for 24 hours. After the reaction, the product was extracted with chloroform, water was removed, and the product was precipitated in methanol. Poly [1,3-propanedioxy-1,4-phenylene-1,2- ethenylene- (2,5-bis (trimethylsilyl)) was obtained. -1,4-phenylene) -1,2-ethenylene-1,4-phenylene] (P-1-1) was synthesized.

Using the polystyrene as a standard, the P
The molecular weight with respect to -1-1 was measured and shown in Table 1. The number average molecular weight was 2,100 and the weight average molecular weight was 7,200. Further, the polymer P-1-1 was excited using a 330 nm xenon lamp as a light source, and the light emission (PL) spectrum emitted from the polymer was recorded and shown in Table 1. Emitted. Here, a lock-in type having a chopping frequency of 150 Hz is used.
) Recordings were made using a PerkinElmer LS-50 fluorescence system using an amplifier.

Preparation of Light Emitting Diode 1.2 g of the obtained P-1-1 was dissolved in 12 ml of cyclohexanone, and then filtered with a microfilter to remove dust. Next, the ITO formed on the substrate
After the layer was washed with an ultrasonic cleaner, the solution was spin-coated on the ITO layer while rotating the substrate at a speed of 4000 rpm for 15 seconds to form a polymer layer having a thickness of 140 nm. Finally, the light emitting diode of the present invention was manufactured through a process of forming a rectangular electrode having a diameter of 5 mm by coating aluminum by a vacuum deposition method.

The wavelength of light emitted from the aluminum electrode toward the ITO electrode was measured by applying a voltage of 25 V through each electrode of the manufactured light emitting diode, and the results are shown in Table 1.
The wavelength was 470 nm and was in the blue region. Here, the wavelength of light was measured using a double-grating monochromator (Spex 270M) equipped with a photomultiplier tube (Hammatuz R955) as a detector.

Example 2 3.02 g of 2-trimethylsilyl-1,4-xylenebis (triphenylphosphonium bromide) (XI-
1) and 1.00 g of 1,3-bis (4-formyl-phenoxy) propane (XII-1), except that poly [1,3-propanediene was used. Oxy-1,4-phenylene-1,2-ethenylene- (2-trimethylsilyl-1,4-phenylene)-
1,2-ethenylene-1,4-phenylene] (P-2-
1) was synthesized.

P-2 produced by the method as in Example 1
After measuring the molecular weight and PL spectrum for −1, a light emitting diode was manufactured and the EL wavelength was measured. Example 3 2.14 g of 2,5-bis (trimethylsilyl) -1,
4-xylenebis (triphenylphosphonium bromide) (X-1) and 1.00 g of 1,5-bis (4-formyl-2,6-dimethoxyphenoxy) pentane (XII)
Poly [1,5-pentanedioxy- (2,6) was prepared in the same manner as in Example 1 except that I-1) was used.
-Dimethoxy-1,4-phenylene) -1,2-ethenylene- (2,5-bis (trimethylsilyl ) -1,4-
[Phenylene) -1,2-ethenylene- (3,5-dimethoxy-1,4-phenylene ) ] (P-3-1) was synthesized.

P-3 produced in the same manner as in Example 1.
After measuring the molecular weight and PL spectrum for −1, a light emitting diode was manufactured and the EL wavelength was measured.

Example 4 2.00 g of 2-trimethylsilyl-1,4-xylenebis (triphenylphosphonium bromide) (XI-
1) and 1.00 g of 1,5-bis (4-formyl-2,
6-Dimethoxyphenoxy) pentane (XIII-1), but using the same method as in Example 1 but using
Poly [1,5-pentanedioxy- (2,6-dimethoxy-1,4-phenylene) -1,2-ethenylene- (2
-Trimethylsilyl-1,4-phenylene) -1,2-
Ethenylene- (3,5-dimethoxy-1,4-phenylene ) ] (P-4-1) was synthesized.

P-4 produced in the same manner as in Example 1.
After measuring the molecular weight and PL spectrum for −1, a light emitting diode was manufactured and the EL wavelength was measured.

[0080]

[Table 1]

[0081]

As described above, the polymer produced according to the present invention not only emits blue light, but also has excellent solubility in an organic solvent, and the blue light emitting diode produced by using the polymer emits high light.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a general light emitting diode.

FIG. 2 is a view schematically illustrating a process of performing electroluminescence when an electric field is applied to the light emitting diode of FIG.

[Explanation of symbols]

 1 ... substrate, 2 ... positive electrode, 3 ... polymer material, 4 ... negative electrode.

Continued on the front page. (72) Inventor Hwang Dao, 371-1, Jungseong-dong, Yuseong-gu, Daejeon, Chungcheongnam-do, South Korea No. 99 Dong, Habitt Apartment 132 Building No. 1302 (72) Inventor Shiku Same Shi South Korea, Gyeonggi-do Seongnam-si, Bundang-gu 320635 (JP, A) JP-A-9-35870 (JP, A) JP-A-9-35871 (JP, A) Macromolecules, 26 [5] (1993), p. 1188-1190 Proc. SPIE-Int. SoC. Opt. Eng. , 3148 (1997), p. 139-150 Doctoral Dissertation Thesis of the Ecliptic, (Department of Chemistry, Korea Institute of Science and Technology, 1995) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08G 16/00-16/06 12 C08G 65/00-65/48 WPI / L (QUESTEL) CA (STN) REGISTRY (STN)

Claims (6)

(57) [Claims] 1. A blue light emitting polymer represented by the following general formula (IV) and having a weight average molecular weight of 5800 to 13000: However, in the above general formula (IV), X is the following formula (V) or (VI), and X
In the following formula (V), Y is the following general formula (VII) or (VIII), Z is the following formula (V), n is 3 , and m is X is the following formula (VI); Y is the following general formula (VII) or (VIII); Z is the following formula (IX); Is 5 and m is 5 to 100; Embedded image Embedded image Embedded image Embedded image However, in the above general formulas (VII) and (VIII), R ₁ , R
₂ and R ₃ are each a methyl group. 2. The blue light emitting polymer is poly [1,3-propanedioxy-1,4-phenylene-1,2-ethenylene- (2,5-bis (trimethylsilyl) -1,4-).
(Phenylene) -1,2-ethenylene-1,4-phenylene]. 3. The blue light-emitting polymer is poly [1,3-propanedioxy-1,4-phenylene-1,2-ethenylene- (2-trimethylsilyl-1,4-phenylene).
-1,2-ethenylene-1,4-phenylene], the blue light-emitting polymer according to claim 1, wherein 4. The blue light-emitting polymer is poly [1,5-pentanedioxy- (2,6-dimethoxy-1,4-phenylene) -1,2-ethenylene- (2,5-bis (tri methylsilyl ) -1,4-phenylene) -1,2-ethenylene- (3,5-dimethoxy-1,4-phenylene ) ]. The blue light-emitting polymer according to the above. 5. The blue light-emitting polymer is poly [1,5-pentanedioxy- (2,6-dimethoxy-1,4-phenylene) -1,2-ethenylene- (2-trimethylsilyl-1,4). -Phenylene) -1,2-ethenylene-
(3,5-dimethoxy-1,4-phenylene ) ]. The blue light-emitting polymer according to claim 1, wherein 6. A blue light source is formed on an ITO layer formed on a substrate.
Spin the solution of photopolymer dissolved in cyclohexanone.
Coating to form a polymer layer,
Coated aluminum by vacuum evaporation
Manufacturing method of blue light emitting diode with aluminum layer
A law, the blue light-emitting polymer is represented by the following general formula (IV)
Having a weight average molecular weight of 5800 to 13000
Blue light emitting diode
Production Method: ## STR00008 ## However, in the above general formula (IV), X is the following formula (V), Y is the following general formula (VII) or (VIII), and Z is the following formula (V) , n is 3, m is 5 to 100; embedded image Embedded image Embedded image However, in the above general formulas (VII) and (VIII), R ₁ , R
₂ and R ₃ are each a methyl group.